This invention relates to the manufacture of semiconductor devices, and more particularly to a metallization system for gates, contacts and interconnects in MOS VLSI devices.
In the manufacture of MOS VLSI devices such as high density dynamic RAMs or the like, the use of metal gates and interconnects has become necessary inasmuch as the resistance of the commonly used gate material polycrystalline silicon makes it unsuitable for such high density applications. When the width of the gate, conductors, etc., is reduced to the one micron range, and the thickness also reduced to avoid step coverage problems, then the use of metal instead of polysilicon becomes mandatory. The selection of a single metal to perform the gate, contact and interconnect functions results in a number of compromises. Thus, multiple metal systems have evolved. Yet, the problems of contact resistance, adherance to oxide, process incompatability, electromigration, and other factors have limited the utility of the prior systems due to one or more shortcomings.
It is the principal object of the invention to provide an improved method of making metal-gate MOS VLSI devices, particularly high density memory cell arrays or the like. Another object is to provide an improved contact and interconnect system and metal-gate transistor structure as may be used in very high density memory arrays. A further object is to provide an improved metallization system with low contact and sheet resistance, good adhesion, good electromigration resistance, and minimal process and materials complexity.